Conventionally, manufacturing of a sewing machine needle has been carried out by a press operation such as die press operation or die pressing, flow press operation, or the like in place of metal cutting or machining. However, such a well-known press operation requires a combination of a punching operation, a grinding operation and an abrading operation, with the result that a plurality of different press dies have to be used and the operation is highly troublesome.
Also, the conventional press operation causes burrs to be produced on a blade of the needle due to the use of dies. Unfortunately, removal of burrs is time- and labor-consuming, therefore, the flow press operation or flow pressing which is said to prevent production of burrs on the blade during formation of the needle has been recently proposed, as disclosed in U.S. Pat. No. 4,044,814.
However, in order to form a metal blank into the blade of the sewing machine needle by flow pressing while preventing formation of burrs on the blade, it is essential that a volume of the metal of the blank flowing into a extraneous cavity formed between a pair of dies be reduced to an amount smaller than that of a volume of the cavity. Also, when the amount of the metal of the blank is very insufficient or the blade is formed with a long groove by coining which causes burrs to be formed on the blade, the strength and quality of the needle is decreased, and loss due to inferior products and manufacturing difficulties increase, leading to an increase in manufacturing costs.
Further, formation of a clearance-above-eye of an insufficient depth on the blade causes a loop of a sewing thread to be often formed into a small size when the thread is fed to the needle while being kept somewhat stretched, so that a looper is apt to fail to satisfactorily catch the loop. Thus, mounting of the sewing machine needle on a sewing machine requires troublesome operations such as adjustments of the sewing machine, including timing adjustment, adjustment of a feed dog or the like, so that handling and operation of the sewing machine require much time and labor.